The present invention is related generally to hydraulic cylinders. In particular, the invention is an improved marine engine trim cylinder.
Hydraulic trim systems used with outboard marine (e.g., boat) engines are generally known and in widespread use. Systems of these types include a hydraulic trim cylinder with a trim rod extending therefrom. The trim cylinder is typically mounted to the transom (i.e., rear) of the boat with the distal end of the cylinder rod engaged with a swivel bracket to which the engine is mounted. The trim system is actuated by an operator to extend and retract the cylinder rod to trim (i.e., raise and lower relatively small amounts) the engine. Often, the trim cylinder is part of a larger tilt and trim unit which also includes one or more tilt cylinders for raising and lowering the engine over a larger range of motion.
A ball bearing is sometimes mounted in the end of the trim cylinder rod. In trim units of this type it is the ball bearing that engages the swivel bracket. Unfortunately, when the bearing dries out or corrodes it sometimes will not roll smoothly within its seat during trim operations. Under these circumstances the operator can experience an annoying chatter sound.
There remains, therefore, a need for improved marine engine tilt systems. In particular, there is a need for tilt systems which are not susceptible to the chatter sometimes present in known systems of this type. To be commercially viable, any such system should also be capable of being efficiently manufactured.
The present invention is a marine engine hydraulic trim cylinder which has a reduced susceptibility to chatter of the type sometimes produced by conventional cylinders of this type. The cylinder can also be efficiently manufactured. These features and advantages are provided by the use of a polymer seat for the ball at the end of the cylinder rod. In one embodiment of the invention the ball seat is formed from polyphenylene sulfide (PPS). Trim cylinders with polymer ball seats in accordance with the invention can also be incorporated into tilt and trim units.